``From Late Latinnonna "nun, tutor", originally (along with masculine form nonnus, denoting a man) a term of address for elderly persons, perhaps from children's speech, reminiscent of nana, like papa etc.`` -- nun#Etymology 1

from Lat. nubere "(for women) to marry," akin to nuptial, etc., perhaps originally meaning "(for women in normal copulation) to lie on the back like a succubus, while for men to lie down like an incubus."